Just curious, did you learn coding just for Lust Doll (or general game making) or you have experience in coding then decide to make games? Making plugins sounds pretty tough.
Of course you can! I just noticed there's even a new fan art contest, sadly I'm too late to the party I guess. Still good to hear that my little artwork being appreciated by you!
Edit: typo.
Actually I'll just stating that these artwork are yours to use freely from now on. Whatever you wish whether commercial or not (not saying that they're commercial-worthy lol)!